I have a php script which send email using the email addresses stored in mySQL DB. But Since my website host limit the number of emails sent to 15 / minute, I need to include some kind of delay. Which means, the emailing system shouldn't send more than 15 emails/ minute. Is there a way to do that. Thanks for your help in advance.

A script's maximum execution time (may or may not be modified, depends on your provider) won't allow you to do this. The only way it can be done is by using some sort of crontab and marking the email addresses as "sent" so that every 15 minutes when your script executes that it doesn't send the same email out to the same people..